Could it be PPD?

My baby just turned 5 months. I'm a stay at home mom with a 3 year old as well. In the past week I've just felt this feeling of overwhelming sadness and anxiety. I don't really have a reason to be feeling this way, I love and adore my children and husband. Husband is hardworking and supportive. I feel so absolutely selfish for feeling like this and I'm trying to hide it so hard because I don't want to put this on my husband. 
I'm unhappy, sad, lonely, and I'm struggling so hard to act like I'm ok but I'm not.